1. Technical Field
The present invention relates to an image forming apparatus adapting an electrophotographic developing system and, more specifically, to a process and apparatus for driving an agitator to prevent cohesion of developing material.
2. Related Art
In general, electrophotographic developing systems have been widely used in image forming apparatuses such as copying machines, laser beam printers, LED (light emitting diode) printers, and facsimile machines using ordinary paper. As stated herein, conventional electrophotographic developing systems operate by repeating a cycle of charging, exposing, developing, transferring, and fixing operations in a sequential order.
I have noticed that one problem associated with the operation of such systems relates to the fact that, once a developing operation is completed, the developing material sits idle for a period of time and tends to become coherent or compacted. In certain systems, such as that noted in U.S. Pat. No. 5,055,881 to Fukuchi, entitled Device For Supplying A Toner To A Developing Unit, once toner is fed from a toner cartridge to a toner supply device, an agitating member is operated for a predetermined period of time to agitate the toner. As an elaboration on that concept, U.S. Pat. No. 5,523,832 to Hamamichi et al., entitled Electrophotographic Image Fonning Apparatus With Controlled Mixing Of Developer, discloses an image forming apparatus having a developing device in which the developer standing idle time is measured by a counter once a particular developing operation has ended, and once it is determined that another developing operation is to commence, the determined developer idle time is used to adjust the period of time during which the developer is mixed prior to commencement of the second developing operation. Finally, U.S. Pat. No. 4,977,428 to Sakakura et al., entitled System For Drive Control Of Toner Agitator In Image Forming Apparatus, discloses an arrangement wherein low torque is applied to the agitator on "start up", and then higher torque is applied after a predetermined period of time after "start up".
Other efforts in the art relative to developing apparatus and image forming apparatus may be seen in U.S. Pat. No. 5,353,102 to Sato et al., entitled Two Component Developing Apparatus In A Printer, U.S. Pat. No. 5,317,370 to Kohyama et al., entitled Developing Apparatus Including Means For Collecting Used Developing Agent, U.S. Pat. No. 5,177,546 to Tsubo, entitled Image Forming Apparatus, U.S. Pat. No. 5,134,444 to Tabuchi et al., entitled Image Forming Apparatus, and U.S. Pat. No. 5,124,752 to Kanno et al, entitled Developing Apparatus.
I have found that systems which perform a mixing operation for a predetermined period of time prior to commencement of a developing process (as disclosed in Fukuchi '881), and systems which perform mixing for a period of time determined by the developer standing idle time (as disclosed in Hamamichi et al., '832) do not provide adequate mixing. That is to say, such systems do not agitate the toner or developing material frequently enough so that, when agitation commences, an excessive amount of torque is required. Since such an excessive amount of torque can exceed the system driving torque provide in the engine mechanism, this can cause damage to the motor in a form of gear abrasion, printing impossibility, paper jam, and so forth. Moreover, the reliability of the apparatus is reduced.
If the image forming apparatus is a facsimile machine utilizing general paper or a complex device, a user cannot transmit or receive the fax document for a long time. In addition, often the printing operation cannot be performed for a long time after turning on the laser beam printer. Thus, the electrophotographic developing processor of the image forming apparatus cannot perform an operation for a long time. I have found that with designs found in such contemporary exemplars require more torque than the torque for agitating the toner due to compaction of the toner as a result of non-usage for a long time. That is, since the density of the toner becomes greater, even if the agitator agitates the toner of equal size. Consequently, more force is required to agitate toner which has more weight and is compacted and coherent.
As a result, when driving an agitator to distribute the compacted toner, the torque required exceeds the system driving torque provided in the engine mechanism, thereby causing damage to the motor in the form of gear abrasion, printing impossibility and paper jams, among other malfunctions, thus deleteriously reducing the reliability of the apparatus.